Muffle furnace



H. N. IPSEN MUFFLE FURNACE Nov. 10, 1953 Filed June 18, 1951 2 Sheets-Sheet 1 Nov. 10, 1953 H. N. IPSEN 2,658,744

MUFFLE FURNACE Filed June 18, 1951 42 Sheets-Sheet 2 Q-qyrold YL-Tp m I AM, v a m? mav/ Patented Nov. 10, 1953 UNITED STATES PATENT OFFICE MUFFLE FURNACE Harold N. Ipsen, Rockford, 111.

Application June 18, 1951, Serial No. 232,158

6 Claims.

The present invention relates to fired heat treating furnaces of the type in which articles to be treated are heated in a hollow muffle disposed within the furnace.

One object of the invention is to bring about a more uniform heating of the furnace muffle through improvements in the distribution of heating gases around the mufile effected by a division of the streams of burning gases entering the furnace from theburners and a redirection of a portion of the gases toward certain areas of the muflle which have heretofore been improperly heated.

In connection with the foregoing, another object is to eliminate hot spots on the muffle and thereby avoid one of the major factors which has heretofore produced overheating of contiguous interior portions of the muffie and tended to cause deterioration of the muffle.

Other and related objects are to produce a more uniform heating effect on objects within the muflle and to increase the operating efliciency of the furnace.

A particular object is to provide a conversion unit which can be conveniently incorporated into furnaces already in use so as to improve their operation in accordance with the invention.

The objects of the invention thus generally set forth, together with other objects and ancillary advantages are attained by the construction and arrangement shown by way of illustration in the accompanying drawings, in which:

Figure l is a vertical sectional view taken along the line l-l of Fig. 2 and showing a muiile furnace embodying the present invention.

Fig. 2 is a vertical sectional view taken along line 2-2 of Fig. 1.

Fig. 3 is a perspective view showing a gas distributing block constructed in accordance with the invention.

Fig. 4 is an exploded, fragmentaryperspective view showing a gas distributing block and a section of the furnace wall having a burner opening and gas distributing recess therein and indicating the relationship of these parts when in assembled position.

Fig. 5 is a fragmentary sectional view taken generally along line 5-5 of Fig. 1.

Fig. 6 is a schematic view showing the relationship to each other of the gas distributing blocks as assembled in the furnace. v

The present invention is applicable to fuel burning mufile furnaces of various specific de- .i ns and constructions. Hence, it will be understood that there is no intention to limit the invention to its application to furnaces of the exact design shown in the drawings and described herein. On the contrary, it is intended to cover all embodiments and alternative constructions of the invention falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more particularly to the drawings, the muille furnace ll), selected for the purpose of illustrating the instant embodiment of the invention, comprises a shell H defining a large internal chamber I2. As shown, this shell is formed from thick heat insulating panels including a floor [4, spaced side walls l5, and a ceiling l6. A hollow muffle l'l formed from adjoining bottom, side, and top panels Ill-2|, is supported in the chamber 12 in spaced relation to the contiguous furnace panels. The muflle panels with the opposed furnace panels define gas passageways 22 extending under the muflie and passageways 24 extending upwardly and around the mufile. Heating of the mufile i1 is eifected by burners 25 mounted in openings 26 extending through the opposed furnace side walls l5 in general alinement with the passageways 22 under the muffle IT.

The furnace thus formed is of a conventional design generally used in the heat treating art. Experience in the operation of such furnaces has revealed that the heating effect of the furnace gases on the mulile I! has heretofore been concentrated on limited areas of the muflle panels. Accordingly, these areas have been overheated while other portions of the muflle have not been adequately heated. In particular, the bottom panel l9 of the mufile has been overheated by the burning gases sweeping under the mufile I! while the side panels 20 have been poorly heated by an uneven flow of cooled gases passing up through the passageways 24.

This unevenness in the heating of the mufile has not only tended to cause deterioration of the muflle but has brought about a non-uniform heating of the objects heat treated in the furnace. It will be understood that non-uniformities in the temperature to which the objects are raised produces consequent variations in the physical characteristics imparted to the objects by the heat treating process.

In accordance with the present invention a more uniform heating of the mufile I1 is brought about by dividing the streams of burning gases entering the furnace chamber [2 from the burners 25 and diverting portions of the gases upwardly through the contiguous passageways 24' while directing the remaining portions of the gases through the passageways 22 under the mufile.

Implementation of the invention is effected by placing in front of the respective burners 25 gas dividers or bafiles 21 which are especially constructed to divide the streams of burning gases and bring about an effective heating of the side panels while at the same time avoiding overheating of the bottom panel IS. A deflecting surface 29 is formed on each bafiie 21 to extend upwardly from an intermediate level relative to the stream of gases which issues from the adjacent burner and is effective to divert u wardly the top portion of this gas stream to heat the contiguous mufile side panel 20. In the illustrated embodiment of the invention the lQWer extremities of the deflecting surfaces 29 are on a level with the extended axes of the burner openings 26 in the furnace walls, but it will be understood tha the r ati ei ht o the e ext emitie an be va ied i dif er t fur aces to. b in abou the mo t ei c ent div on o eases et een he. ho zontal ga na eee'eways 2 and the vertical passa eways. 24.-

n the p efe re construc ion illustrate Z ea h baffle 21 comprises an upright elongated blocl; of refra tory ma ri the lowe nd oi wh ch c mprises. an en ar ed base adapted t rest n. th fur ace lo r 14 and pro ect a sh rt d stance into the inner end oi he adjac n one f th bu ner op nin s '25, igs- 1 nd he outer ide face of each baflle block. .21 i curved inward y from he top of the base 3!! to orm e defl ctin surface 2.9 of: the hafliei As, sh w thi ur a e i cu ed rathe sharply at its lower nd but straightens out toward s upper nde Thev central por ion. of the base 36 f each baffle block 2. isiormed w t a d wnwar ly pen rectan u ar recess .31, facin t e furnace oor l4 and extending from the fro tto the back s d o the block- The rece s hus p ovided d fines a transverse channel throu h which burn n ases are directed into the passageway 22 e t ndin under the burner. Preferably, the, channel re-t. cess 3| of each'baffle block extends upwardly to the. lower end of. the deflectin urface 2% the roof of the channel. intersecting the Surface to define a clear cut gas dividin e ee. 32, Figs 3. and 5.

As shown, the channel recess 31 of each baflie 7 base 3.]! is substantially equal in widthv to, the

diameter of theadiacent one of the orifices at of the burners 2.5, Ei eii a d 5.1 Struc ural mate! rial: of each base on opposite eideex fi the base recess 3!. forms two oppos d depend n support; less 35. which test on th u ac floor IL I will be obse ved. that. the streams of burnin canes which new from the channels 31' hrough the horizontal passageways .22 are e filolently remov d f om the bot om, nu ile panel 1a to preen the formation oi h tenote on. thepaneI, while at the came tim eiiective y ating the. panel to operating t mpe atures! In etaneee such he pres nt one, in which the iunace burners the e employed n opposite eide o he furna i l. th enacted-burn rs. are normal y. oca ed. in. sta g red rela ion to each other- This ship o thehurnersis shown. E ga 1 and. but it an b better visualized wi h ret r nce to Fla, e which hows the. relative locati n. of; the baflle blocks. 2.!- as disposed in front o ith re pective: burners.

Taking cognizance of this. staggered burner are rangemeht. further provision isv made. in accorde ance with the invention for effecting a greater lateral dispersion of the burning gases diverted upwardly by the bailies 21. For this purpose the deflecting surfaces 29 of the bafiles are given a small lateral twist or curvature which acts to spread the hot gases entering the vertical passageways 24 laterally over the muflle side panels 20. Preferably, the direction of twist of each deflecting surface 29 is such that the gases passing over the surface are directed to the side of the associated burner 25 lying across from the Qpposed burner on the opposite side of the furnace.

In instances in which the baffles 21 are incorporated into furnaces at the time they are built, the side walls of the furnace are preferably formed with recesses 36 which extend upwardly and laterally from the inner end of each burner opening 26 for cooperation with the bafiles in expediting the direct distribution of burning gases into'the verti al pass eway 24- As shown in Figs. 1, 2, 4, and 5, the recesses 3.6 are g nerall fan-shaped and progressivel decrease in. lateral pth longi in lly of the burners 25. from the lower ends of the recesses which intersect the burner openings 26 to the upper extremities of the recesses. which extend somewhat above the baffles 21. It will be noted that the recesses. 35" gradually increase in width to extend laterally to one side of the burner openings 26. tov conform in shape to the flow lines of the gases" diverted upwardly and laterally by the respective baflleszll.

It will be understood that'the invention is susceptible of being used with furnaces. already in operation as. well as in new furnaces. The bafile blocks 21 provided by the invention form conversion, units which may be incorporated intoconventional furnaces of the type described without any substantial modification of thefurnaces.

As shown in Figs. 1 and 5, the burners 25 of conventional furnaces are commonly provided" with rather large burner blocks 31 which fit di rectly into the burner openings 26. 'To permit the installation of the baille blocks 21- into a furnace, the burner blocks it! are removed from theburner openings which usually are formed to have a rectangular or square-transverse shaping. The baffle blocks 21 are then inserted longitudinally through theburner openingsZG anderected in front of the burner openings, as shown in, the drawings. The burners including the blocks. 31 are replaced and the furnace isagain readied for operation with the baffles 2'! assembled in working positions.

If desired the recesses 36 can be dug into the furnace walls i5 by working throughthe burner. openings 26. However, significant improvements in the operating characteristics ofthe furnace are realized when the distribution blocks are used without the cooperating recesses 36;.

It will be evident that the elimination of hot spots on the furnace muffles prolongs the Direct the mufiies. At the same time, it achieves a more even distribution of heat. to the mufiie withthe result that the physical properties imparted to objectsheat treated'in furnaces equipnedwith the invention areirnproved' and mad more uniform. Moreover the uniform distribution ofgheat makes practical the use ofa silicon carbide structural material in the fabrication of the muille s, it being understood by those in the art thatthe properties of silicon carbide as used in these muffles have certain advantages in themselves provided the material is protected-from excessive and spotty heating as it is by the invention.

Other worthwhile accomplishments attributable to the invention include increases in the heating and operating efficiency of muffle furnaces which stem from the improved distribution of burning gases about the furnace muffles.

I claim as my invention: i l i 1. A mufille type heat treating furnace comprising, in combination, a plurality of adjoined furnace walls including a floor wall and an adjoined side wall defining an internal chamber, a hollow, muffle disposed in said chamber in spaced relation to certain ones of said furnace walls including said floor wall and said side wall so as to define a first gas passageway under said muffle and a second gas passageway between said muffle and said side wall, a fuel burner in said side wall and substantially alined with said first passageway, a combustion gas distributing member disposed between said burner and the contiguous portion of said mufile and comprising an upright elongated block having an enlarged base and a vertically elongated upper portion, said base including spaced downwardly extending support legs resting upon said floor wall and cooperating with the body of said block to define a transverse channel extending through said base from the front to the back side thereof for permitting one portion of the combustion gases issuing from said burner to flow through said block into said first passageway, and said elongated upper portion of said block having an inwardly and upwardly curved deflecting surface facing said burner and extending upwardly from the vicinity of the upper portion of said channel to divert directly into said second passageway a second portion of the gases from said contiguous burner.

2. A muffle type heat treating furnace comprising, in combination, a plurality of adjoined furnace walls including a floor Wall and opposed side walls defining an internal chamber, a hollow muffle disposed in said chamber in spaced relation to certain ones of said furnace walls including said floor wall and said side walls so as to define combustion gas passageways under and around said muffle, a plurality of burner openings extending through said opposed side walls in staggered relation to each other and having burners therein substantially alined with the passageway under said muffle, a plurality of combustion gas distributing members equal in number to said burners and individually disposed between said respective burners and contiguous portions of said muffle, each of said members comprising an upright elongated block having an enlarged base extending a short distance into the inner end of the contiguous burner opening and including spaced downwardly extending support legs resting upon said floor wall and cooperating with the body of said block to define a transverse channel extending through said base from the front to the back side thereof, and extending upwardly to the level of the extended axis of the contiguous burner thus permitting one portion of the combustion gases which issue from said contiguous burner to flow through said block into said passageway under said muffle, each of said blocks having an elongated upper portion extending vertically above the base of the block and defining an inwardly and upwardly curved deflecting surface facing the contiguous burner and diverting directly into the contiguous one of said passageways between said side walls and said muffle a second portion of the gases which issue from said contiguous burner, said deflecting surfaces on said respective blocks being slightly twisted laterally so as to disperse said second portions of gases laterally in wide streams in opposed relation to staggered burners in the opposite furnace side wall.

3. A muffle furnace comprising, in combination, a plurality of furnace walls defining an internal chamber, a hollow muffle disposed within said chamber in spaced relation to certain ones of said furnace walls so as to define therewith combustion gas passageways extending under and around said muffle, one of said walls defining a burner opening located in contiguous relation to the lower portion of said muflle, the inner face of said one wall defining a recess therein extending upwardly from the inner end of said burner opening said recess gradually decreasing in its lateral depth and gradually increasing in its lateral width from its lower to its upper end, an upright bafile supported in said furnace between the inner end of said burner opening and said muflle, means on said baffle defining a gas defiecting surface extending upwardly from the vicinity of the extended axis of said burner opening, said deflecting surface being disposed in spaced relation to the opposed bottom surface of said recess and serving to deflect a certain portion of the gases entering through said burner opening upwardly between said muffle and the contiguous one of said furnace walls and at the same time permitting the remaining portion of the gases to flow under the muffle between the muffle and the lower one of said furnace walls.

4. A muffle type heat treating furnace comprising, in combination, a plurality of adjoined furnace walls defining an internal chamber, a hollow muflle disposed in said chamber in spaced relation to certain ones of said furnace walls to define therewith combustion gas passageways under and around said muffle, a plurality of fuel burners disposed on one of said walls in general alinement with said passageway under said muffle, a plurality of combustion gas distributing members equal in number to said burners and individually disposed between said respective burners and contiguous portions of said muffle, each of said members comprising a block of refractory material having a transverse channel defined in the lower end thereof and extending through said block from the front to the back side thereof for permitting one portion of the combustion gases issuing from the contiguous burner to flow through said block into said passageway under said muflie, the upper portion of each of said blocks having an upwardly extending deflecting surface thereon facing the respective burners and extending upwardly to divert directly into said passageway between said one furnace side wall and said mufile a second portion of the gases from the contiguous burner, and said deflecting surface on each of said blocks being slightly twisted laterally so as to disperse said second portions of gases laterally in wide to said burners and disposed between said are snective (burners and said muflie, each of said 'bafiles defining a deflecting surface having nne edge in the stream of gases issuing from the asljacent one of said burners and extending upwarflly from said edge with a twisted curvature to flireet one 'portion of the gas stream upwardly and laterally into the passageway between said one wall and said muffle While permitting another of the stream to flow under said edge and through the passageway under said muffle.

6. A combustion gas distributing member "for use in a muffle type heat treating furnace, :said member comprising a block of refractory material adapted to be disposed in al'inement with'a furnace burner, and means on the lower porbion of said block defining an elongated channel extending from the front to the back side of the 8 block to permit :the passage at La nortinn 'oi the combustion gases therethmngh, thefront side 9f said block defining a deflecting surface extenfim upwardly above said ehannel andztwistedjlaterally to deflect another portion of the gases upwardly and laterally relative to the block.

HAROLD N.- IPSEN.

References Cited in the file of this patent UNITED JSTATES PATENTS Number Name Date 901,956 Creighton Oct. 27, 1908 1,172,222 Muckle Feb. '15, 1916 2,216,809 Derby Oct. *8, 11940 FOREIGN PATENTS Number Country Date 434,948 Great'Britain Sept. 9 1-935 

